MHB Finding x in Logarithmic Equation

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The discussion revolves around solving the logarithmic equation log2(2^(x-1) + 3^(x+1)) = 2x - log2(3^x), leading to the solution x = -1.70951. Participants outline steps to manipulate the equation using logarithmic properties, ultimately equating logs to simplify the expression. The transformation results in a form that can be approached with numerical methods, as an algebraic solution is not feasible. The final consensus confirms the numerical solution aligns with the provided answer. The discussion emphasizes the complexity of solving logarithmic equations and the utility of numerical methods in such cases.
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Hi, sorry if it's not in the right subforum. idk how to solve x:
http://puu.sh/2Lbb1.png
The answer is x = -1.70951.
how do we get there? please explain everystep. thanks :3

****someone made it this far, idk if it is the correct path:
log2 (2^(x-1)+3^(x+1)) = 2x - log2 (3^x)
log2 (2^(x-1)+3^(x+1)) + log2 (3^x) = 2x
because of the rule log(m) + log(n) = log(mn),
log2 ((2^(x-1)+3^(x+1))*(3^x) = 2x
log2 ((2^(x-1)+3^(x+1))*(3^x) = 2x
log ((2^(x-1)+3^(x+1))*(3^x) / log 2 = 2x
log ((2^(x-1)+3^(x+1))*(3^x) = 2x * log 2
log ((2^(x-1)+3^(x+1))*(3^x) = log 2^(2x)
equate the logs
(2^(x-1) + 3^(x+1))*(3^x) = 2^(2x)
2^(x-1) * 3^x + 3^(2x+1) = 2^(2x)
3^(2x+1) = 2^(2x) - 2^(x-1) * 3^x
 
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Re: logarithm

Seems like kind of a struggle, but you are getting good practice playing with the logarithms.

I might do this:

\log_{2}\left(2^{x-1}+3^{x+1}\right) = 2x - \log_{2}\left(3^{x}\right) = \log_{2}\left(2^{2x}\right)- \log_{2}\left(3^{x}\right) = \log_{2}\left(\dfrac{2^{2x}}{3^{x}}\right)

This leads a little more quickly to a version with no logs which may not be as useful as you think.

2^{x-1} + 3^{x+1} = 2^{2x}\cdot 3^{-x} = \left(\dfrac{4}{3}\right)^{x}

There is no way to solve that, so you are really left with numerical methods, which probably causes you to reintroduce the logarithms.

Can you take it from there?

I get x = -1.70951129135145, which certainly agrees with your given solution.
 
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